Sealing system for a vertically disposed shaft

ABSTRACT

A sealing system for an essentially vertical shaft includes an active sealing element disposed between a first structural part rotating with the shaft and a second structural part stationary on a housing. A wall of the housing separates an upper oil-free volume from a lower volume containing oil. The oil flows through the sealing system through a gap formed by the first structural part and a third structural part stationary on the housing. The active sealing element is preferably a threaded shaft seal. In another embodiment, the active sealing element is a combination of a primary contact seal and a threaded shaft seal. The oil flow removes heat generated by the rotating system.

BACKGROUND OF THE INVENTION

The invention relates to a sealing system disposed in the aperturethrough a housing wall, for an essentially vertical shaft with an activesealing element which is disposed between a structural part rotatingwith the shaft and a structural part stationary on a housing, with thehousing wall separating an upper, oil-free volume from a loweroil-containing volume.

Sealing systems of this type are used for example in a vacuum pump suchas is described in DE-A-42 33 142. In the case of vacuum pumps of thistype the elimination of the heat generated in the rotating systempresents problems. It develops, for one, due to the compression work ofthe rotors in their suction chambers and, for another, through the heatdue to friction of the contact seals (radial shaft sealing) used.

SUMMARY OF THE INVENTION

The present invention addresses the problem of creating a sealing systemof the above cited type in which the elimination of heat issignificantly improved.

This problem is solved according to the invention thereby that throughthe sealing system flows oil and that the structural part rotating withthe shaft as well as a further structural part stationary on the housingform a gap through which the oil flows. The oil flowing through this gapabsorbs, for one, heat from the structural part rotating with the shaftand eliminates it. For another, the oil establishes a heat contactbetween the rotating structural part and the structural part stationaryon the housing so that via the structural part stationary on thehousing, and thus via the housing, the heat is eliminated.

The structural part and the further structural part stationary on thehousing are usefully realized in the form of a labyrinth in theirregions facing one another for the purpose of extending the gap throughwhich the oil flows. The cooling effect is thereby enhanced. Inaddition, a long gap of this type has the effect of a choke. Thismaintains excess pressure and thus continuous flooding without bubbleformation at the oil inlet.

The active sealing element can be a contact sealing (shaft seal, collarsealing or the like) or a threaded shaft seal. Especially useful is acombination comprising a primary contact seal and a second threadedshaft seal as auxiliary sealing.

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a sealing system with a threaded shaftseal according to an embodiment of the invention.

FIG. 1a shows a sectional view of a sealing system with a threaded shaftseal according to a variation of the embodiment of FIG. 1.

FIG. 2 shows a sectional view of a sealing system with a threaded shaftseal according to an embodiment of the invention.

FIG. 3 shows a sectional view of a sealing system with a threaded shaftseal according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In all Figures the housing wall is denoted by 1, an aperture provided inthe housing wall 1 by 2, a vertical shaft penetrating the aperture 2 by3, and a sealing system sealing the shaft 3 against the aperture 2 ingeneral by 4. The housing wall 1 separates for example in vacuum pumpsan upper oil-free volume (suction chamber with low pressures, vacuum)from a lower oil-containing volume (gearing chamber, in which pressuresexceeding the atmospheric pressure can occur). In the embodimentexamples depicted the shaft 3 is supported in the aperture 2. Bearingsdisposed underneath the sealing system 4 are denoted by 5.

The sealing system 4 comprises a structural part 7 rotating with theshaft. Furthermore, two structural parts 8 and 9 stationary on thehousing are present. The first structural part 8 (sealing structuralpart 8) encompasses the rotating structural part 7. The secondstructural part 9 stationary on the housing forms together with therotating structural part 7 a gap 11 through which flows oil. The supplyof the oil, preferably PFPE oil, which is under slight excess pressure,takes place via a bore 12 in the housing wall 1. Subsequently, as willbe explained later in further detail, it flows through the gap 11 andarrives through the bearing 5 in the oil-containing volume disposedunderneath the bearing 5.

In the embodiment example according to FIG. 1 the rotating structuralpart 7 and the sealing structural part 8 stationary on the housing forma threaded shaft sealing 13. The threads disposed on the rotatingstructural part 7 are implemented such that with the shaft rotating oilpenetrating from below into threaded shaft seal 13 is again transporteddownwardly (recirculating threads). The oil rises at a given pressuredifference in the recirculating threads until an equilibrium is reachedbetween the pressure difference to be sealed off and the recirculatingpressure of the threads. The variable level of fill must remain lessthan the geometrically available axial length of the recirculatingthreads.

The second structural part 9 stationary on the housing (gap-formingstructural part 9) comprises a flange-form edge 14 extending below thestructural part 8 and a cylindrical segment 15 extending upwardly at thelevel of the rotating structural part 7. This segment 15 extends free ofcontact into an annular groove 16, open in the downward direction, inthe rotating structural part 7, and specifically such that the gap 11 isformed.

During operation of a machine with a sealing system 4 according to FIG.1 the oil flows from the bore 12 through radial slots 18 into an annularvolume 19 in which the recirculating threaded gap 13 as well as also gap11 terminate from above. Oil reaching the threaded gap 13 iscontinuously carried back in order to ensure the desired sealing. Theoil can therefore only flow out of the annular volume 9 through gap 11,thus moving between the rotating structural part 7 and the cylindersegment 15 initially upwardly and subsequently again downwardly. In thisway it fulfills the task of absorbing heat from the rotating structuralpart in order to eliminate the heat itself or to transfer it to thestructural part stationary on the housing. The width of the gap isusefully smaller than 1 mm, preferably 0.3 mm.

In the case of using the solution according to FIG. 1 in a vacuum pump,the following must be considered: if the pump is stored while it isstill warm from operation (for example at 80° C. and thus at a gearingvolume pressure, generated by thermal expansion, of approximately 1.3bars), the recirculating pressure of the threaded shaft seal 13diminishes instantaneously. Consequently the persisting gearing volumepressure will force the oil contained in the threaded gap upwardly intothe delivery volume of the pump. In order to solve this problem, it issuggested to provide an expanded annular volume 21 above therecirulating thread 13 (depicted in FIG. 1a) in which in the describedcase the oil can be collected without penetrating in fact into the pumpvolume. When the pump is started again, the threads immediately returnthe oil in the expanded annular volume 21 unless the oil has returned byitself after a relatively long standstill in connection with the coolingof the gearing volume.

In the embodiment example according to FIG. 2, in addition to thethreaded shaft seal 13, a contact seal is provided and specifically aradial shaft sealing ring 22 (RSSR 22). It is disposed in the annularvolume 19, and specifically underneath the threaded shaft seal 13. Itsdisposition is selected such that its sealing lip 23 together with therotating structural part 7 forms an--internally located--sealing site.The open side of the sealing ring 22 faces the oil-containing volume.The spacing of the sealing site from the gap 11 through which oil flowsis as small as possible so that an effective cooling of the sealing siteis achieved. In this embodiment example, RSSR 22 initially seals off theoil in conventional manner. In order to attain optimum service life ofthe RSSR 22, a low specific radial force, preferably less than 0.15N/mm, should be ensured. For this purpose the RSSR 22 can be installedwithout a spring. In contrast to conventional configurations, the RSSR22 runs on a thin-walled tubular extension of the rotating structuralpart 7. This allows for the contacting sealing site to be cooledespecially strongly from the inside and from the outside. Due to the lowradial force, on the one hand, and the cooling of the sealing site, onthe other hand, a considerable increase of the service life of the RSSR22 can be expected in contrast to conventional dispositions of RSSR.

As soon as a leak occurs on RSSR 22 which goes beyond the holdingcapacity of the annular volume 19 above the RSSR 22, the recirculatingthreads 13 become active. The higher the oil rises with further leakagein the recirculating threads 13, the higher becomes the liquid pressuregenerated by the threads on the topside of the RSSR 22. Thereby the RSSR22 becomes increasingly free of loading and finally runs nearly free offriction. Nevertheless, when the pump is taken out of operation, if thepressure of the threads diminishes, the RSSR 22 seals the gap againcompletely so that no oil can be pushed through in the upward directionthough the excess pressure in the gearing volume. An oil collectionvolume 21, as was described in connection with the solution according toFIG. 1, can thus be omitted. During the next start, the threadsimmediately transport the oil in the downward direction. In the process,the RSSR 22 is lubricated from above and simultaneously the load isremoved. If, in the pump which in the meantime has cooled, the pressurein the gearing volume is still relatively low, the RSSR, impressed fromabove, can allow oil to penetrate downwardly whereby the recirculatingthreads can potentially become partially or completely pumped empty. Inaddition, during the start, the RSSR 22 prevents that oil adhering onthe sealing gap walls from being suctioned upwardly into the deliveryvolume of the pump.

In the embodiment example according to FIG. 3 a PTFE collar seal (PTFEcollar 24) is provided as a primary contact seal. An advantage of thisprimary seal, compared to the RSSR 22 according to FIG. 2, is thegreater pressure bearing capability and thermal stability of the PTFEshaft sealing ring. For the remainder the configuration and thefunctions of this solution correspond to the solution according to FIG.2.

As described, the sealing system 4 comprises a rotating structural part7 and two structural parts 8 and 9 stationary on the housing. Thesecould each comprise several parts or be an integral component of theshaft 3 or the housing wall 1. In the last case, however, theirfabrication is difficult. This applies in particular to the rotatingstructural part 7. In the embodiment according to FIG. 3, due to annulargroove 16 which could otherwise only be produced with difficulty,rotational structual parts comprises two essentially cylindrical parts71, 72 which are connected by means of shrink-fitting or hard-solderingand which form the annular groove 16 between them.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments, and that various changesand modifications may be effected therein by one skilled in the artwithout departing from the scope or spirit of the invention as definedin the appended claims.

What is claimed is:
 1. A sealing system for use in a vacuum pumpequipped with a vertical shaft, said sealing system comprising:astationary housing; a vertically disposed shaft mounted for rotationwithin said housing; a seal means connected to said shaft for rotationwith the shaft within said housing, said seal means having a top and abottom surface, said seal means includes a rotating threaded shaft sealhaving an outer surface, said outer surface adjacent an inner surface ofsaid housing and forming a first space; a cylindrical groove within saidseal means extending upward from the bottom surface; and a cylindricalsegment disposed within said groove to provide a gap between adjacentsurfaces of the groove and the segment which creates a flow path,whereby cooling oil can be conducted through said flow path, saidcylindrical segment being connected to said housing.
 2. The sealingsystem of claim 1, including an expanded annular volume disposedadjacently above said first space.
 3. The sealing system of claim 1,wherein said first space is in communication with said gap through anannular volume, said oil being able to flow into said gap, into saidannular volume, and into said first space.
 4. The sealing system ofclaim 1, including a second seal, said second seal being a radial shaftsealing ring disposed below said rotating shaft seal.
 5. The sealingsystem of claim 1, wherein said oil is introduced into a lower portionof said first space for an upward directional flow, and wherein saidrotating threaded shaft seal provides a recirculating pressure thattransports said oil back into a downward directional flow as said oilrises through said seal.
 6. The sealing system of claim 1, including asecond seal, said second seal being a collar seal disposed below saidrotating shaft seal.
 7. The sealing system of claim 1, including asecond seal, said second seal being a contact seal.
 8. The sealingsystem of claim 7, wherein said contact seal is disposed in an annularvolume below said rotating threaded seal, and wherein said contact sealseparates the lower entrance of the first space with the entrance of thegap.
 9. The sealing system of claim 7, wherein said contact seal has alow specific radial force.